In high average power magnetrons, the cathode is generally subjected to high levels of incident energy. When this energy is present during normal operations, it creates a large temperature gradient across the cathode structure which causes damage if not dissipated. In the prior art, cathode heaters have been developed to conduct heat to the cathode. The cathode may then be at operating temperature upon start up of the magnetron.
A commonly used prior art cathode heater is of the "soldering iron" type. A soldering iron cathode heater uses a coated filament wire which is wound on a solid rod connected to the emitter. The wire is heated by resistive losses when a voltage is coupled to the wire. The heat is then conducted through the rod to the emitter. However, soldering iron cathode heaters present numerous disadvantages and limitations. Such heaters cannot be heated rapidly. The normal warm-up time for such heaters can be as much as five minutes. If the temperature of the wire is too hot, its coating will burn, thereby causing the magnetron to fail. A further disadvantage and limitation with soldering iron cathode heaters is the large thermal mass required, which is unacceptable for many applications where weight savings is a critical factor. Thus, it would be highly desirable to provide a high speed, low weight cathode warm-up heater for high average power magnetrons.